Alert device for attaching to radio receiving sets



May 1, 1956 M. AUERBACH 2,744,194

ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS Filed June 21, 1951 5Sheets-Sheet l INVENTOR.

y 1, 6 I M. AUERBACH 2,744,194

- ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS Filed June 21, 1951v 5 Sheets-Sheet 2 INVENTOR.

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y 1, 1956 M. AUERBACH 2,744,194

ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS 4 Filed June 21, 1951s Sheets-Sheet 5 I Q ,J ma

VEN W MMHL MLZ E 5. 5. 142M, fl 0m United States Patent ALERT DEVICE FORATTACHING T0 RADIO RECEIVING SETS Martin Auerbach, Flushing, N. Y.

Application June 21, 1951, Serial No. 232,772

4 Claims. (Cl. 250-) This invention relates to an alerting device whichis adapted to be attached to an ordinary radio receiving set.

An object of the invention is to provide an attachment for a radioreceiving set which does not atfect the ordinary operation of the setbut which can be controlled by a broadcasting station to produce warningsignals in case of fires, air-raids, special news bulletins and variousother emergency conditions.

Another object of the invention is to provide an alerting device for aradio receiving set that can be attached to the set without requiringadditional soldering or the services of a radio technician to installit.

Another object of the invention is to provide an alerting device with astand-by arrangement the operation of which can be controlled by abroadcasting station.

Another object of the invention is to provide an alerting device,requiring no additional radio tubes, for attaching to a radio receivingset by merely plugging into said set.

. These objects and others ancillary thereto are accomplished bymodifying a radio receiving set by a plug-in adapter unit that attachesto the sets audio circuits and which has a silent or stand-by switchthat does not normally allow any sound to come from the loud speaker.However, upon the broadcasting station sending out a warning signalwhich may be a steady tone for 30 seconds for example, a trigger'devicein the adapter unit is actuated to turn on the speaker and allow thesound or message to blare forth. The triggering device may be of varioustypes such as a neon tube, a superregenerative relay, a cold cathodetube or a squelch circuit. These triggering circuits are all operated bya voltage building up to a predetermined value. However for aneconomical device and reliable operation a bimetallic strip which bendson the application of heat generated in a coil wound about the strip isvery satisfactory. The heat that bends the bimetallic strip far enoughto either make or break a contact is supplied by the audio signal whichis received by the set from the warning tone signal. One phase of thisinvention is based on the dis covery that the customary broadcast musicor sound fluctuates in value so that it does not heat the bimetallicstrip suliiciently to bend the strip far enough to make or break thecircuit whereas a steady tone signal can cause the bimetallic strip soto bend. It is also possible and sometimes desirable to introduce acircuit which selectively degenerates the audio stage so that all audiotones other than a particular one or a particular narrow range of tonesare reduced in value so that only the preselected tone will operate thebimetallic strip. When the bimetallic strip makes or breaks a contactmeans are operated to turn on the loud speaker, etc.

The device may be connected to the set by one. or more plug-ins in atleast two different ways. First one or more of the tubes can be removedand a plug having sockets for receiving the tube in its upper portionmay be inserted the original tube socket. Second the device may2,744,194 Patented May 1, 1956 provide separate sockets for one or moreof the tubes of the set and in this case the tube or tubes are removedfrom the set, inserted in the sockets provided on said device and aclosed top plug connecting the set to the device is placed in theoriginal socket of the set.

The bimetallic strip of the device is surrounded by a coil which heatsto cause the bimetallic strip to bend from its normal position when theoperating cycle tone is received. The said bimetallic strip may itselfmake or break contact with an electrical circuit to operate anotherrelay or switch or the bimetallic element may operate a mechanicalswitch. Once the switch is thrown by the bimetallic element it isdesigned to be locked in position so that the alerting device does notcease to operate unless manually turned off. The operating switch isalso desirably constructed as to turn on other warning signals such asbells, lights, vibrators, etc. A very satisfactory and economical typeof mechanical switch that is readily operated by a bimetallic strip isthe preloaded spring switch.

A very satisfactory way to cut out the loud speaker in the stand-bysetting is to connect a shunt across the primary terminals of the outputtransformer. In order to be able to plug in the device of the inventionand have the plugs of the device provide a connection between theterminals of the primary of the transformer it is sometimes necessary toemploy two plug-in means one being inserted in the tube socket occupiedby the audio output and the other being inserted in the socket occupiedby the rectifier tube.

In climates or places where ambient temperature may become high enoughto operate or affect the bimetallic,

the variations in ambient temperature may be compenwill be compensatedwithin the bimetallic element or elements.

The novel features characteristic of this invention are Y set forth withparticularity in the appended claims. The invention itself, however,both as to its organization and its method of operation, together withadditional objects and advantages thereof, will best be understood fromthe following description of specific embodiments when read inconnection with the accompanying drawings in which:

Fig. 1 is a circuit diagram of the device of the invention including thespeaker and two tubes of the receiving set to which it is attached.

Fig. 2 is a rear view of a small receiving set illustrating how thedevice is attached to a receiving set.

Fig. 3 is a bottom view of an adapter unit as actually constructedshowing the switch device after it has been thrown by a bimetallicstrip.

Fig. 4 is a detail view showing the switch device before being thrown.

Fig. 5 is a top plan view of the bimetallic unit and switch of Figs. 3and 4.

Fig. dis a side view of a modified form of bimetallic strip.

V Fig. 7 is a top plan view of the device of Figs. 3-5.

Fig. 8 is a side view of the same.

Fig. 9 is a view similar to Fig. 7 of a modified form of the device.

In the diagram of Fig. 1, the portion included in the v box A is theportion of the receiving set which is adapted or altered in thetransformation to a set with the alerting device of the presentinvention. The tube 10 is the rectifier tube of the set and tube ll isthe power output tube. It will be seen that the line 13 from the cathodeconnection 12 of tube is connected to one side of the transformer 21 ofthe speaker at point 14, for example, so that by means of an auxiliaryplug it is possible to provide a connection between wire 15 of thealerting unit and the lower side of the transformer 21 without requiringthat the wire 15 be soldered by the purchaser of one of the alertingunits.

Input line 16 from the previous tube of the set connects to the grid ofthe power output tube and the anode connection 17 of this tube isordinarily connected to the opposite side of transformer 21 at 18, forexample, but in the device of the invention the output connection 17 isconnected to the switch electrode S2 and to the line which in turn isconnected to coil 31 so that the A. C. component (the audio tone) willpass through to heat the coil 31 but the D. C. voltage will not passthrough condenser 36. The coil 31 surrounds the bimetallic element 32which is held at one end 33 upon the chassis of the attachment (seeFigs. 4 and 7). From the coil 31, a line 34 connects through a variableresistor 35, line 37, switch contacts S-9 and 8-1, line 15, and point 14to the lower side of the primary 21 of the speaker. When the switch S isin the position shown (the standby position) the primary 21 thereof isshunted and the speaker silenced by line 37, switch contacts S-9 and S-1and line 15; however any signal that is received by the radio set ispassed by line 30 through the coil 31. Ordinary signals received fromthe standard broadcasting stations fluctuate in value too much to causethe coil 31 to heat up sufiiciently to make the bimetallic element 32bend but a sustained audio frequency note or tone of constant amplitudewill cause the coil 31 to heat the bimetallic element sufficiently tocause it to bend and throw the switch S. The length of time required forthe received audio frequency signal to heat the coil 31 sufficiently tobend the bimetallic 32 can be adjusted within wide limits (from a fewseconds to several minutes, for example) by the variable resistance 35.Thus the variable resistance 35 is not an absolute requirement of thesystem but contributes to the effectiveness of the device. A choke coil39 is also inserted between lines 30 and 37 to increase the voltageacross coil 31 although this choke 39 is not absolutely necessary. Thespring 40 which operates the switch S when moved by bimetallic 32 isshown only diagrammatically in Fig. 1.

The additional switch elements 8-3 to 8-8 and 8-10 to S12 are similarlynot absolute requirements for the system but serve helpful and desirablefunctions. The contact 8-10 is connected in the position shown to a deadpoint 8-3 but when rod 8-13 is moved upwardly by spring element 40, 8-10contacts S4 and thereby connects the main line to the plug 51. A lightor a bell or any other signalling device may be plugged into the plug51. It should be mentioned that when the audio signal passing throughcoil 31 causes the bimetallic 32 to throw the switch S, therebyconnecting the loud speaker and disconnecting the shunt across thelatter, the signal audio-tone which is being transmitted blares forthfrom the speaker for as long a time as it is continued. But additionaldevices which may be more effective may be attached through the plug 51.

The third switch element from the bottom S5, S-6 and S-11 operates tomake only one audio tone or a narrow range of audio tones effective toheat the coil 31 and operate the bimetallic 32 and switch S. As shownthe output connection 17 is connected to line 52 thence, to contact S-5,contact S-ll, line 56, condenser 53, tank circuit 54 (consisting ofinductance 55 and condenser 56), and line 57 to the input line 16 oftube 11. The tank circuit 54 acts as a degenerative feed back toeliminate all signals except those to which the tank circuit is resonantor substantially resonant. Thus the device may be made to be operated byany desired narrow range of frequencies by selecting the proper valuesof coil 55 and condenser 56. While this particular element is notnecessary to the operation of the remainder of the circuit it can beseen that it does increase the possibilities of the device since varioussets may be made effective for different signals which different signalsmay be employed for a variety of different purposes. The contact 8-6 asshown is dead.

The top set of contact elements 8-7, 8-8 and S-12 act to cut down thepower required during the stand-by position and to prolong the life ofthe tubes. Since the tubes of the set are to be maintained in operatingcondition at all times in the stand-by position they obviously wear outin less time than required for normal operation of the radio set. Withthe switch in the stand-by position shown the normal power of the line50 is not ap plied to the heater elements of the tubes but instead acertain amount of the power is dissipated in resistance 69. Thus theheater circuit is fed from the main line 50, line 60, resistance 60 andline 62 the contact element 8-? being dead. When the switch S is thrown,however, the resistance 60 is shunted by contacts S-8 and S12. It isobvious that resistance 60 cannot be too large since the set must stillbe able to receive and amplify the audio frequency signal for operatingthe bimetallic 31.

One other unrequired but desirable feature, shown in the lower righthand side of Fig. 1 is a hand operated testing attachment 65, 66. A pushbutton 65 for example may be provided to connect the coil throughresistance 66 to a signal adapted to heat coil 31 and thereby find outwhether said coil 31 and bimetallic element is working. The normal D. C.plate voltage supplied at 68 for example will pass through resistor 35,coil 31 and resistor 66 to ground 67 through push button 65 therebyheating up bimetallic strip 32.

After the switch S is thrown from stand-by position it is locked inoperating position and can be returned manually to the stand-by positionof Fig. 1 by a handle 70 such as shown in Figs. 3 and 4 for example.

Fig. 1 illustrates the circuit employed but one advantage of the instantinvention is that it can be plugged into an ordinary radio set withoutrequiring a skilled mechanic to install it. Thus no soldering, orsimilar operation which is unfamiliar to the ordinary radio user isrequired. All one need to do is to remove one or two tubes, place theplugs of the attachment where the tubes were and then placing the tubesin the sockets of the attachment provided therefor. Figs. 3-9 thereforeillustrate one of the simplest of the commercial forms of the unititself and Fig. 2 shows how the unit is attached to a small radio set.Fig. 2 shows a receiving set 9 having tubes 10' and 11 shown in phantomcorresponding to tubes 10 and 11 of Fig. 1. To install the attachingunit which is shown in Figs. 3-8 tubes 10 and 11' are removed and placedin sockets and 81 respectively (see Fig. 7) and plugs 82 and 83 are thenplaced in the sockets 7 and 8 provided on the set 9 as shown in Fig. 2.No attempt is made to trace all the lines running from the plugs 82 and83 since such a showing would only confuse and since these lines may beconnected in many ways which are all within the skill of an ordinaryradio mechanic, to produce the circuit of Fig. 1. It is obvious that theline from the particular socket in tube socket 8 with which connection17 is made will not go directly to the corresponding socket in tubesocket 81 of the unit but instead will be connected (1) to a lineleading to 8-2 and possible S-5 and (2) to the line 30. For the mostpart however the individual sockets in tube socket 7 or 8 will bedirectly connected to the corresponding sockets in the tube socket 80 or81 by means of plug 82 or 83 and lines 84 or 85. With tube 10, forexample, all the individual sockets of tube socket 7 may be directlyconnected to all the corresponding sockets in tube socket 80, the onlychange necessary being that an additional line 15 is connected to thesocket making connection 14 in the tube socket 80. If the modificationis to include resistance 60 and its circuit an additional socket is mod-.ified.

In the figures of the drawing like numbers refer to like parts. Thus inFig. 3, which is a bottom view of an at-' tachment 100 mounted inhousing 90, the tube sockets 80 and 81, the plug socket 5.1, the mount33 for the bimetallic element 32, the choke coil 39, the resistance foradjusting the time for response of the bimetallic element 32 are allshown. The resistance 35 has a control knob 35 extending outside ofcasing 90. For simplicity the wiring connections in the attachment areomitted from Figs. 3-9.

A typical spring switch device is shown in Figs. 3-5. The bimetallicelement is shown in standby position in Fig. 4and in released positionin Fig. 3. The switch S of this element is only a two part one insteadof the 4- part switch of Fig. 1 and the switch 5' of Figs. 3 and 4 is inreversed position relative to Fig. l. The switch is operated by a pairof arms 91, 92 and the spring 40. In the position shown in Fig. 4 theinside arm 92 which is attached to one end of the semicircular spring isabove the arm 91. Any movement ofthe arms 91, 92 toward each othercompresses the spring 40. Once the arm 91 is moved slightly above thearm 92 the spring 40, being compressed, tends to snap the arm 91 furtheraway from the arm 92 to the position shown in Fig. 3. In the deviceshown in Figs. 3 and 4 the bimetallic element 32 is arcshaped atordinary temperatures and tends to straighten out if heated. Theinflexible member 8-13 of the switch S is attached to the arm 92 and ismoved downwardly by said arm to cause contacts S-9 and 8-10 to engagewithcontacts S-2 and 8-4, respectively, as shown in Fig. 3.

Contact 84 is connected to plug 51 and contact 8-2 is connected as shownin Fig. l. The spring 40 holds or retains the switch S in the positionshown in Fig. 3 until it is returned manually to the stand-by positionof Fig. 4 by pulling handle 70 which slides in the bearing 93. Thespring 40 is pivotally attached to the arms 91, 92 in any way such as bythe small projections 94, 95 which fit into small openings (not shown)at the ends of spring 40. The end of arm 91 is, of course, movedupwardly by the end of bimetallic element 32.

In climates where there are wide changes of temperature it is possiblethat the temperature changes may be sufiicient to cause the bimetallicelement 32 to bend and thereby move arm 91 when no alerting signal hasbeen received. This is not often the case since room temperatures varyonly slightly in modern homes and since the coil 31 can be made powerfulenough and the bimetallic element 32 insensitive enough to avoid anysubstantialv I movement due to ordinary temperature changes. However,when such changes are significant the device shown in detail in Fig. 6may be substituted. In this figure the bimetallic element 32 is made ofS-shape and the coil 31 is placed only around one half of the 8 so thatchanges in room temperature do not affect the position of the end 96 ofthe bimetallic element since one half of the 8 element compensates forchanges due to difference in ambient temperature in the other half ofthe 8. Since the coil 31, however, only surrounds half of the 8, it iseffective to cause the bimetallic element to bend when the proper signalis passed therethrough.

A modified type of unit is shown in Fig. 9. Here instead of the simplepulgs 82 and 83, plugs 101 and 102 are employed. For this unit the tubes10 and 11 are removed, the plugs 101 and 102 are placed in the socketswhich previously held the tubes 10 and 11 and the tubes 10 and 11 arethen placed into the socket provided at the top of plugs 101 and 102.Here not as many wires are required to connect the plugs 101 and 102 tothe elements in casing 105. One additional connection 106 to ground isdesirable. Otherwise the device of Fig. 9 is identical with that ofFigs. 38.

It may be noted that in some radio sets, it would not be necessary toemploy a device with two insertable plugs 82 and 83. That is, one plug82 for the tube 10 could be omitted since it is possible in some sets toshort out the primary 21 of the transformer by connecting the line 15,etc. from the conection 19 of tube ll to 8-1, etc.- This can be donewhen connection 19 is taken directly from point 14. However, in manycircuits the screen grid connection 19 is not at point 14 potential butinstead a resistance is inserted between the point 14 and the connector19. In order to have an attachment which works for all sets it isdesirable to make said attachment with two'plug-in means 82 and 83.Substantially all receiving sets are so constructed that point 14 isavailable from a pin connection from the socket for tube 10. It may alsobe noted that in Fig. 4 the normal position of the bimetallic element 32is shown as curved and that the heating of the element 32 by the coil 31causes the said curved element to straighten out. It is equally aspractical to employ a bimetallic element which is normally straight andwhich bends when heated.

It will be readily seen that the invention provides an attachment'for aradio set that can be readily attachedby unskilled persons and thatthesaid attachment is effective, inexpensive and economical in use.

I claim:

1. An alerting device for attachment to radio receiving sets of the typehaving a transformer operated loud speaker and at least one audiofrequency amplifier tube including a power tube which operates thetransformer, comprising shunt means adapted to be connected to shunt outthe primary of the loud speaker while permitting the tubes of said setto operate, snap switch means movable manually to connect and disconnectsaid shunt across the primary of said transformer, bimetallic meansresponsive to a particular sustained audio frequency tone received bysaid radio set to snap said switch means from shunt-connecting toshunt-disconnecting position when sensitized by said sustained audiofrequency tone, said bimetallic means being insufliciently affected bynormal broadcast signals to operate said snap switch, and a degeneratingfeed back circuit adapted to degeneratively feedback from the output ofthe power tube to an input of an audio frequency tube all but apredetermined range of frequencies, said snap switch means comprises amultiple pole switch having a first set of contacts disconnecting saidshunt and another set of contacts disconnecting the feed back circuitwhen said switch is operated by said bimetallic means.

2. An alerting device for attachment to radio receiving sets of the typehaving a transformer operated loud speaker comprising shunt meansadapted to be connected to shunt out the primary of the loud speakerwhile permitting the tubes of said set to operate, snap switch meansmovable manually to connect and disconnect said shunt across the primaryof said transformer, bimetallic means responsive to a particularsustained audio frequency tone received by said radio set to snap saidswitch means from shunt-connecting to shunt-disconnecting position whensensitized by said sustained audio frequency tone, said bimetallic meansbeing insufliciently affected by normal broadcast signals to operatesaid snap switch, and a resistance adapted to be connected in serieswith the cathode heating line for said tubes when the said shunt isconnected to the primary of said speaker and in which said snap switchis a multiple pole switch having a first set of contacts disconnectingsaid shunt and another set of contacts shunting said heating lineresistance when said snap switch is operated by said bimetallic element.

3. An alerting device for attachment to radio receiving sets of the typehaving a transformer operated loud speaker comprising shunt meansadapted to be connected to shunt out the primary of the loud speakerwhile permitting the tubes of said set to operate, snap switch meansmovable manually to connect and disconnect said shunt across the primaryof said transformer, bimetallic means responsive to a particularsustained audio fre quency tone received by said radio set to snap saidswitch means from shunt-connecting to shunt-disconnecting position whensensitized by said sustained audio frequeney tone, said bimetallic meansbeing insufficiently afiected by normal broadcast signals to operatesaid snap switch, said bimetallic means including a heating coil and avariable resistance in the heating coil circuit adapted to control thetime of the response of the bimetallic element.

4. An alerting device for attachment to radio receiving sets of the typehaving a transformer operated loud speaker comprising shunt meansadapted to be connected to shunt out the primary of the loud speakerwhile permitting the tubes of said set to operate, snap switch meansmovable manually to connect and disconnect said shunt .across theprimary of said transformer, bimetallic means responsive to a particularsustained audio frequency tone received by said radio set to snap saidswitch means from shunt-connecting to shunt-disconnecting position whensensitized by said sustained audio frequency tone, said bimetallic meansbeing insufiiciently affected by normal broadcast signals to operatesaid snap switch, said bimetallic means including a heating coil and amanually operated push button adapted to connect said heating coil witha source of power of sufiicient energy to test the operation of the saidbimetallic means.

References Cited in the file of this patent UNITED STATES PATENTS2,033,492 Stone, 11'. Mar. 10, 1936 2,055,921 Baker Sept. 29, 19362,104,844 Ailel Ian. 11, 1938 LE -0,75 eal Feb. 1, 1944 2,353,499Purington July 11, 1944 2,367,378 Schick Jan. 16, 1945 2,447,156Brittain Aug. 17, 1948 2,531,416 Fel'rar Nov. 28, 1950 2,552,331 LambMay 8, 1951 FOREIGN PATENTS 526,239 Great Britain Sept. 13, 1940

